1. Field of the Invention
This invention relates to electronic medical devices that are implanted in the body of a patient. More particularly, it relates to a congestive heart failure monitor for detecting and monitoring the progression of congestive heart failure and the method of remote control and communication with the device.
2. Description of the Related Art
Many patients who have suffered one or more myocardial infarctions subsequently require treatment for congestive heart failure (CHF). The left heart fails while the pumping function of the right heart remains adequate, because the latter has only about 20% of the workload of the former. This leads to an increase in blood volume congested to the lungs, resulting in pulmonary congestion, build up of increased levels of fluid, and congestion of internal organs including the stomach and intestines. Increased fluid in the stomach and intestines reduce their ability to absorb drugs prescribed for treatment of CHF, particularly diuretics. The congestion is often accompanied by a worsening of myocardial function, with consequent drop in blood pressure and reduced renal perfusion, which only further aggravates the congestive situation. Thus, late recognition of congestion leads to increased dosages of oral diuretics that are unsuccessful to treat the condition, ultimately requiring that the patient be hospitalized.
Avoidance of hospitalization and the pitfalls of late treatment require detection of CHF at an early stage, so that the prescribed drugs can be fully absorbed and effective. If detected early, a combination of diuretics and other drugs can slow the progress of the disease and allow the patient to enjoy an improved lifestyle.
An extensive review of telemonitoring for the management of heart failure by Louis et al. has been published in the past in the European Journal of Heart Failure. The conclusion of this article is that telemonitoring might have an important role as a strategy for delivery of effective health care for patients with heart failure. However, the current state of the art still lacks an adequate means to monitor the data and to communicate data.
The ApexPro FH enhances patient safety by using a bidirectional, frequency-hopping infrastructure to help ensure that patient data is transmitted clearly and completely to a central patient monitoring station. While this system is based on external data and provided by GE Healthcare using a Unity Network, the use of the medical implant communication service band is not part of the system nor is an implantable device considered to be part of the communication system. This system relies rather on data external to the patient.
Several patents have looked into impedance monitoring and data processing and monitoring and diagnosing hypertension or congestive heart failure in patients. Among those is Riff, U.S. Pat. No. 5,876,353 which describes an Impedance Monitor for Discerning Edema through Evaluation of Respiratory Rate. U.S. Pat. No. 5,957,861, Combs et al. and its continuation, U.S. Pat. No. 6,512,949 describes an Implantable Medical Device for Measuring Time Varying Physiologic Conditions Especially Edema and for Responding Thereto. The U.S. Pat. No. 6,104,949, Pitts Crick et al. relates to a device and method used for the diagnosis and treatment of congestive heart failure. Specifically, this invention senses a trans-thoracic impedance as well as patient posture and correlates changes in posture with trans-thoracic impedance in order to assess the degree of congestive heart failure. The Device for Detecting Pericardial Effusion, Godie et al., U.S. Pat. No. 6,351,667 describes an apparatus for detecting pericardial effusion that includes a measurement apparatus connected to a wire probe to be anchored to the right heart ventricle and two other wire probes to measure the impedance between different probes in order to assess the degree of pericardial effusion. U.S. Pat. No. 4,899,758, Finkelstein et al., describes a Method and Apparatus for Monitoring and Diagnosing Hypertension and Congestive Heart Failure, by using C2 and brachial artery pulses to discriminate a threshold of certain Windkessel function. U.S. Pat. No. 6,336,903, Bardy et al. relates to an automatic system and method for diagnosing and monitoring congestive heart failure and outcomes thereof. A plurality of monitoring sets are retrieved from a database and each patient's status change is tested against an indicator threshold corresponding to the same type of patient information as the recorded measures to which it was compared. The indicated threshold corresponds to a quantifiable physiological measure of a pathophysiology indicative of congestive heart failure. U.S. Pat. No. 6,416,471, Kumar et al., describes a Portable Remote Patient Telemonitoring System. This invention has useful application to the connection of patient data during drug trials and medical testing for regulatory approvals as well as the management of patients with chronic disease. U.S. Patent Publication No. 2002/0115939, Mulligan et al. describes an Implantable Medical Device for Monitoring Congestive Heart Failure in which incremental changes in a parameter data over time provide insight into the heart failure state of the patient's heart.
None of those previous disclosures however describes adequate means to communicate those signals in a safe way between an implant device and an external data handling and coordinating center.
It is a principal aim of the present invention to provide an implantable heart failure monitor which is capable of achieving very early detection of CHF. It is a further aim of the present invention to describe the method of remote controlling an implanted diagnostic or therapeutic electronic device in uni- or bi-directional ways.